A Kiwi woman who once dated the British Prime Minister and was a socialite before joining a convent is a happy, 'naughty nun', says a long-time friend.

Laura Adshead attended St Margaret's College in Christchurch before moving to the UK where she went to Cheltenham Ladies' College and Oxford University, the Daily Mail reported.

While there she met the future Prime Minister David Cameron in the late 1980s and the pair dated for more than a year.

After the break-up Ms Adshead moved to New York where she became lost in a life of drink, drugs and partying before becoming a Benedictine nun at Abbey of Regina Laudis in Connecticut in 2008.

The 44-year-old, now Sister John Mary, is part of a documentary called God is the Bigger Elvis about the convent she joined.

However, not everything has changed it seems.

A former classmate and long-time friend of Ms Adshead said while her perspective on life had changed, her personality hadn't.

The pair kept in regular contact, and last year Shelley Spang spent 10 days with her at the abbey.

"She's got that sparkle and the wicked sense of humour she always had. We nicknamed her the naughty nun - I won't tell you why,'' she said.

Ms Spang knew the former socialite during her partying days and earlier, while she was dating David Cameron.

"We used to meet on a Friday for drinks at Sloane Square. He was just a young conservative then and she was going out with him.''

"It just came to its natural end.''

After learning Ms Adshead had taken her vows, Ms Spang decided to visit her at the convent "to see it for myself''.

She said her friend was "just happy, just at peace'' at the convent where she was in charge of the rose gardens as well as other daily tasks.

Ms Adshead's parents were very proud of their daughter's decision to join the convent, said Ms Spang. Her father Sam Adshead died a week after seeing her take her vows and his ashes had been scattered at the convent grounds, she said.

Another friend who knew Ms Adshead during her school days in Christchurch said she always stood out but never expected she would become a nun.

"She was quite something. Very very pretty, very bright, she was very sharp and you just couldn't not notice her,'' said Jacqui Rogers.

At age 16 after she had moved to the UK, Ms Adshead returned to New Zealand for a visit and still turned heads, she said.

"She floated into the common room looking worldly, elegant and poised whilst we all gaped at her in awe.

"She was always going to be in that sort of society, but I knew she didn't like to talk about the fact she came from NZ,'' said Mrs Rogers.

In the documentary Ms Adshead speaks about how her life has changed.

"I did think my life would progress on the normal tracks of meeting someone, marrying, having children, but that's not the path that God has led me.''

"I feel like I tried most things in life that are supposed to make you happy. That journey took me down into alcoholism and drug addiction,'' she tells the documentary.

She joined the abbey after coming into contact with Christianity when she joined Alcoholics Anonymous.

"A monastic life, this is where the struggle is,'' she said in the documentary.

"It's like this hothouse where things get worked out.''

The main subject of the film is prioress Mother Delores, 73, who was formerly Hollywood star Dolores Hart, who kissed Elvis Presley when she appeared opposite him in two films.